1. Field of the Invention
This invention relates to a speed change control method and device of an automatic transmission for a vehicle provided with an electronic control for controlling oil pressure supply to a hydraulic servo for a friction engaging device according to electric signals.
2. Description of the Prior Art
In a prior automatic transmission to maintain the drivability, at a low engine temperature, a speed change to a predetermined high speed stage (speed change stage producing reduction gear ratio lower than a predetermined value) is prohibited at the low temperature of the engine irrespective of vehicle speed. However, when the vehicle proceeds rapidly to high speed travelling after starting the engine, the output of the engine is sufficiently large so that no obstacles against the drivability are encountered in the travelling at the high speed stage. Namely, in the prior automatic transmission, the vehicle is driven at the low speed stage even through in such a case disadvangages are produced such as inefficiency of fuel comsumption and restraint in noxious exhaust gas component production.